Testing apparatus



H. FLETCHER AND F. J. STRASSNER.

T S NG APPARATUS.

APPLIC 0N FILED JULY I4, 1920.

1386,69 4 Patented Aug. 9 19211,

A Freyuengy in periods o'er second untrsrnrasleranr arise.

HARVEY FLETCHER,

or NEW YORK, N..Y., NEw JERSEY, ASSIGNORS To WESTERN AND FRANK J. ST'RASSNER, 0F NEWARK, ELECTRIC COMPANY, INCORPORATED, OF

NEW YORK, N. Y., A CORPORATION OF NEW YORK. p

TESTING APPARATUS.

To all whom it may concern: r

Be it known that we, HARVEY FLETCHER and FRANK J. STRASSNER, citizens of the United States,'residing at New York, in the county of New York and State of New York, and at Newark, in the county of Essex and State of New Jersey, respectively, have invented certain new and useful Improvements in Testing Apparatus, of which the following is a full, clear, concise, and exact description.

This invention relates to new and useful improvements in testing apparatus. It has, therefore, as its object, the provision of a test set wherein transmitters and receivers may be efficiently and rapidly tested to determine both the transmission efficiency and quality of such instruments.

It has for years been well known that when a receiver and transmitter are connected electrically, with the receiver in close proximity to the mouth of the transmitter, a current is generated which produces a hum or singing tone. \Vhen the transmitter and receiver are separated by an inclosed air column, a tone of a definite pitch will be emitted and the potential difference measured across the terminals of the transmitter will-vary in accordance with the agitation of the transmitter diaphragm.

In a series of experiments conducted by Messrs. Kennelly and Upson of Harvard University, a report of which may be found in the proceedings of the American Philosophical Society, volume 47, of May-August, 1908, No. 189, beginning on page 329, .it was found that the efliciency of a receiver and transmitter coupled by an inclosed air column could be determined by measuring the value of the resistance necessary to be inserted inthe electrical coupling to damp out the singing tone produced by the combination.

The present invention pertains to an improved method especially applicable to the commercial testing of such instruments whereby they may be rapidly tested in large quantities.

For accomplishing the above object, the

invention provides a test set arranged to test rapidly and efiiciently'both transmitters .-,nd receivers. The test set is equipped with a pair of tubes or couplers each of which is designed to connect a transmitter with a Specification of Letters Patent. Patent d A 9 1921 Application filed July 14,

1920. Serial No. 396,115.

receiver. In the preferred form of the invention, these tubes are of metal, but any other suitable composition of tube may be provided without departing from the spirit and scope of the invention. These tubes are positioned in the set in such a manner that the transmitter is held with the face upward at an angle of approximately 20 with the 'vertical. The purpose of this is to subject the instrument under test to substantially the same conditions as when it is actually in service. The transmitter that is desired to be tested is coupled by means of one of these tubes with a standard receiver. The receiver under test is likewise coupled with a standard transmitter. T hesevarious sets of instruments are also connected electrically by means of sui'tabie circuit connections so that they are in a tone producing relation. In this way, transmitters and receivers are tested.

A better understanding of the invention may be had from the following description when considered in conjunction with the accompanying drawing, wherein Figure 1 shows the test set partly in section, together with the circuit connections employed, while Fig. 2 shows a series of curves representing the behavior of various transmitters of different characteristics. I

In Fig. 1, there is shown a casing 4t having a compartment 5, wherein the circuit connections are adapted .to be positioned. To one side of the casing 4 and on the inside thereof, a member Gris secured. Upon this member 6 there is mounted a standard transmitter 7 which fulfils certain requirements both as to the transmission efficiency tually in service. Although in this particular set, the transmitters are shown as being held in position by means of blocks 9, any

other suitable means may be provided.

On the upper surface of the casing 4, there is secured a member 10 which stands .verti caliy and upon which a pair of metal tubes 11 and 12 are positioned. One end of these tubes formed in the shape of a .cup for" the purpose of receiving a receiver of any of the well known types. The other end of these tubes is straight and is adapted to be shaped ends of each of p which there is associated a battery'22. The

' duced which more nearly simulates that of mined reading on the volt-meter 26.

secured to the transmitter in the same manner as the mouth piece. In order that various tests may be performed, the tubes are made telescoping. In this way, the length of the tubes and the air column may be varied to alter thereby the conditions under which the transmitters and receivers are adapted to be tested.

The cup shaped ends of each of these tubes have inserted therein, a cushion of felt such as indicated at- 15. This felt is provided for the purpose of making the connection between the receiver and the tube as nearly air-tight as possible. The receivers are adapted to, be held in position in the cup the tubes by means" of suitable clamping springs 13 and '14 respectively.

. Associated with the tube llriS a receiver 16 which is 'of the bi-polar type and is known to have a definite efliciency. The receiver shown in the drawing and designated by the numeral 17 is one which is to be tested. This receiver is coupled by means of the tube'12 with the transmitter T, "the transmission etficiency and quality of which has previously been determined. There is also provided an additionalreceiver 18, the purpose of which will be more clearly brought out in the description which is to follow.

A brief description of the apparatus having been given. it is thought that the invention willbemore clearly understood from a description of the method employed in testing the instruments for which the set was designed.

In the first instance. let it be assumed that it is desired to test boththe transmission 'efliciency .and quality of a transmitter.

This is accomplished by first adjusting the value of the current flow through a resistance 19 which is normally connected *in bridge of the conductors 20 and 21 with value of the current through the resistance 19 is adjusted to give a deflection of the voltmeter 26 of 10 volts. This is accomplished by means of a variable resistance 23 connected in series with the battery 22. The

resistance element 19 is chosen so that the resistance thereof is substantially the same as that of a standard transmitter while howling. In this way, a condition is pr a test performed in the testingv of a standard transmitter.

The current traversing the resistance 19 having been adjusted to give apredeterplugs 0 and 31 may then be inserted into the jacks- 32 and 33 respectively. The insertion of the tacts of the jack 33 and the plug plugs into these jacks which are a part of the test set, connect through the tip conductors thereof the transmitter 8 and through the sleeve conductors thereof the receiver 17. both of which are desired to be tested. It is, however, understood that it is impossible to test simultaneously both of these instruments. The key 42 is therefore provided. which is arranged to control the connection of the transmitter and receiver in circuit with the conductors'20 and 21. The circuit ceeded with. The connection of the receiver and transmitter in this manner and the passage of a current through the button of the,

transmitter (not shown) produces a bum or singing tone. The circuit including the transmitter may be traced from one terminal of the battery 22. the choke coil27, contact 36 of key 38, conductor 21, contact 10 of key 12, conductor 43, contact 44, tip con- 31, conductor 45 transmitting button (not shown). conductor 46. tip contacts of plug 30 and jack 32. conductors 47 and 20; contact 37 of key 38, the choke coil 28. contact 48 of key 42 and the resistance element 23 to the other side of the battery 22. Bytracing the circuit including the receiver 16 which extends from one terminal of the receiver, conductor 49, contacts 50, 40 of key 42. 0on ductor 43. contact 4-1 of key 42. tip contacts of jack 33 and plug 31, conductor 45. trans- .mitter button. (not shown), conductor 46.

the other terminal of the receiver 16, it is seen that the receiver 16 is connected in parallel relation with the transmitter 8. The

choke coils 27and 28 are provided for the purpose of offering a'high impedance to the alternating current that produces the howling efiect, thereby preventing this current from passing through the battery 22 .and the leads extending thereto. Direct current s, however, prevented from passing through the coils of the receiver due to the condenser 51 connected in the receiver circuit and thereby prevent the receiver from being injured due to the connection of the battery .22 in circuit therewith.

hen the conditions above outlined exist.

the combination produces a hum or singin tone, the pitch of which is controlled by the two instruments.

length of the tube or coupler connecting the the transmitter and receiver when coupled in this manner, are noted, the electrical connections of the receiver are reversed by means of the key 38. This, as is seen, reverses the battery supply with respect to the receiver. Upon the reversal of the circuit connections of the receiver, the transmitter and receiver connected in this manner produce a. diiierent deflection of the voltmeter and a change in the pitch of the tone emitted.

In determining the transmission efficiency of the transmitter, the two readings of the voltmeter are taken into account, that is, the voltage taken across the transmitter terminals with the connections of the receiver normal, is compared with voltage with the connections reversed- The average of these two volt-ages has been found to be a measure of the transmission efficiency of the instrument under test as compared with astandard transmitter.

To test the quality of the instruments it is necessary to utilize a standard transmitter coupled with a standard receiver and note the change in the pitch of the hum or singing tone supply with respect to the'receiver. Inasmuch as it has been found advantageous to have the pitch. of the hum or singing tone increase upon the reversal of. the battery supply with respect to the receiver, should the tone produced upon the reversal of the battery supply be of a lower pitch than before such reversal, the original electrical connections of the receiver must be reversed to thereby reverse the direction of current through the receiver. It is thus possible by comparing the change in the pitch of the tone emitted, with that of a transmitter and receiver of known transmission efliciency and quality when subjected to similar conditions. to determine the quality of such instruments. That is, if .a transmitter of the above character is placed in a tone producing relation and upon the reversal of the battery supply with respect to the receiver a tone of increased pitch is emitted, a transmitter that responds in a similar manner is said to be in good quality, however, if the opposite effect is produced the instrument is said to be poor in quality.-

' It is thus seen from the above description method for effectively testing both thetrans- The pitch of the tone the drawing,

key 38 which reverses the battery supply 22- upon the reversal of the battery mission efiiciency and quality of a trans- 1 mitter.

In testing the efficiency of the receiver,

the receiver 18 is positioned in the cup the plugs 30 and 31 withdrawn trom'their 54 and 55. -With u respective jacks, a. circuit is completed upon the actuation of key 42 which includes the receiver 18 and the transmitter? with the source of battery 22. The current t-ravers-. ing the circuit including these elements is then adjusted by varying the resistance 24 to produce an average deflection of 10 volts of the voltmeter 26 when the battery supply is connected with the receiver as shown in and upon the actuation of the with respect to the receiver, After the current has been adjusted to give such a deflection, the receiver 18 is then replaced by the receiver 17, the transmission efliciency of which is desired, and the plugs 30 and 31 inserted in their respective j acks. The electrical efficiency of this receiver 17 is thus determined in the same manner as that described in connection with the transmitter 8, that is, the average of thevoltage across the terminals o'fthe receiver under normal conditions and when the battery supply is reversed with respect to the receiver, is taken as a measure of the transmission efficiency of such receiver.

There is also provided means whereby the cord connecting the transmitter and receiver with the plugs may be tested for the purpose of testing for short or open circuits which may exist in the cord. In determining this, the key 42 -is thrown to. the left thereby opening contact 44 and closing contacts 58, 59 and 60. The opening of contact 44 disconnects the lead wire extending between the two sides of the key 42, while the closure of contacts 59 and 60 places the resistance element 19 in shunt of the condenser 51 thereby establishing a continuous path which permits the passage of direct current around the condenser 51. The closure of contact 58 connects the conductor 21 to which the battery 22 is connected withthe tip conductor 45 of the lug 31. A circuit is thus established inclu ing the source of potencuitwhich may be present in the cord cir .cuit by noting whether any noise is produced in the receiver.

Referring now to Fig. 2, which shows a d series of curves representing the behavior of various transmitters possessing .diiferent produced in periods against'the tube length in inches. Curve A tube duced by a standard transmitter.

clearly, the method of distitliguishing trans-.

mitters which are considere good in quality and those that are poor in quality. In plotting these curves, the pitch of the tone per second is plotted represents the phenomenon of a hollow transmitter or one "having a low natural period, curve B that of a'standard or transmitter, while curve C represents that of a sharp transmitter or, one having a high natural period. The solid line of these curves is determined by noting the change in the pitch of the tone emitted for various or coupler lengths with the battery supply connected with the receiver terminals ina certain relation. The broken line represents the change in the pitch of the tone emitted upon the reversal ofthe 'bat-' tery supply with respect to the. receiver. From these curves it is seen that the behavior of the various transmitters may be compared with that of a standard transmitter as rep resented by the curve B. 1

In the preferred form of the invention, a tube length of approximately 13 inches is employed. This particular tube length was chosen since a tone is produced. the pitch of which was found to lie about half way between the breaking points of the tone pro- The numeral 62 designates one of these breaking points. It is also evident tion of these curves, that senting a "'hollow" and a ter tend to occupy the area the curves repre- "sharp transmittaken up by the curve representing a good transmitter'as the' quality more nearly becomes that of a good transmitter. It .is also noted that at this tube length the. pitch of the tone produced y a standard transmitter upon the reversal of the battery supply with respect to the receiver as indicated by the dotted line. increases. From this as a basis it isto determine readily the quality of various other instruments. that is. if upon the re .versal of the "batter supply with respect to the receiver. the pitch of the tone increases.

the transmitter is said to be good in quality as compared witha standard transmitter, while if the pitch decreases. it is said to be poor in quality.

What is claimedis:

1. The method of comparatively testing the quality of a. transmitter which consists in connecting such tra mitter ina tone producing relation with a receiver of known transmission efliclency, separating such 1 transmitter and receiver by an inclosed air column, and reversing the electrical circuit after an examine- *"versing the electrical circuit possible of such receiver, whereby the quality of such transmitter may be determined by the'comparison of the pitch of the tone so produced with the pitch of the tone produced when a transmitter of known transmission eficiency and quality is subjected to similar conditrons.

2. The method of. comparatively testing the quality of. a transmitter which consists in electrically connecting such transmitter in parallel relation with a receiver of known transmission eficiency, coupling such transmitter and receiver by a tube whereby they are in a tone producing relation, and revers ing the electrical circuit of such receiver. whereby the quality of such transmitter may be determined. by the comparison of the pitch of the tone 'so produced with the pitch of-the tone produccdwhen a transmitter of known transmission efficiency and subjectedto similar conditions. 7 I 3. The method of comparatively testing the quality of a transmitter which consists in connecting such transmitter in a tone producing relationiwith a receiver of known transmission efliciency. coupling such transmitter and receiver by a tube'of approximately 13 inches. and reversing the electrical circuit of such receiver. whereby the quality of such transmitter may be determined by the comparison of the pitch of the tone so produced with the pitch of the tone produced when a transmitter of known transmission efficiency and quality is subjected to similar conditions.

4. The method of testing the quality of a transmitter which consists in connecting such transmitter in a tone producing relation with a receiver of a known transmission efficiency. separating such transmitter and receiver by an inclosed. air

of such receiver whereby it a tone of an increased pitch is produced upon such reversal the instrument is said to be good in quality.

5. The method of testing the quality of a transmitter which consists in connecting such transmitter in a tone producing relation with a receiver of a known transmission efliciency, receiver by an inclosed air column, and reversing the electrical circuit of such receiver whereby if a tone of a lower pitch is produced upon such reversal the instrument is said to be poor in quality as comparedrwith an instrument 01f known transmission enciencyand quality.

In witness whereof we hereunto subscribe our names this 2nd day of July, A. 1920.

- is VEY'FLETC R.

r*K J. sassa column, and reseparating such transmitter and quality is 

